This paper is an introduction to an elegant and powerful technique in modern optics: Pound–Drever–Hall laser frequency stabilization. This introduction is primarily meant to be conceptual, but it includes enough quantitative detail to allow the reader to immediately design a real setup, suitable for research or industrial application. The intended audience is both the researcher learning the technique for the first time and the teacher who wants to cover modern laser locking in an upper-level physics or electrical engineering course.

http://www.jila1.nickersonm.com/papers/An%20introduction%20to%20Pound-Drever-Hall%20laser%20frequency%20stabilization.pdf

An introduction to Pound–Drever–Hall laser frequency stabilization

Formation and evolution of binary and millisecond radio pulsars

Neutron Stars 1: Equation of State and Structure

We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of 1.5M , a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric (e = 0.44) orbit around an unevolved companion.

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Binary and Millisecond Pulsars

We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make 14 significant measurements of the Shapiro delay, including new detections in four pulsar-binary systems (PSRs J0613−0200, J2017+0603, J2302+4442, and J2317+1439), and derive estimates of the binary-component masses and orbital inclination for these MSP-binary systems. We find a wide range of binary pulsar masses, with values as low as ${m}_{{\rm{p}}}={1.18}_{-0.09}^{+0.10}\,{M}_{\odot }$ for PSR J1918−0642 and as high as ${m}_{{\rm{p}}}={1.928}_{-0.017}^{+0.017}\,{M}_{\odot }$ for PSR J1614−2230 (both 68.3% credibility). We make an improved measurement of the Shapiro timing delay in the PSR J1918−0642 and J2043+1711 systems, measuring the pulsar mass in the latter system to be ${m}_{{\rm{p}}}={1.41}_{-0.18}^{+0.21}\,{M}_{\odot }$ (68.3% credibility) for the first time. We measure secular variations of one or more orbital elements in many systems, and use these measurements to further constrain our estimates of the pulsar and companion masses whenever possible. In particular, we used the observed Shapiro delay and periastron advance due to relativistic gravity in the PSR J1903+0327 system to derive a pulsar mass of ${m}_{{\rm{p}}}={1.65}_{-0.02}^{+0.02}\,{M}_{\odot }$ (68.3% credibility). We discuss the implications that our mass measurements have on the overall neutron-star mass distribution, and on the "mass/orbital-period" correlation due to extended mass transfer.

/pdf/the-nanograv-nine-year-data-set-mass-and-geometric-fnmk7hcqdj.pdf

The NANOGrav Nine-year Data Set:Mass and Geometric Measurements of Binary Millisecond Pulsars

The stable rotation and sharp radio pulses of PSR 1937+21 make this pulsar a clock whose long-term frequency stability approaches and may exceed that of the best atomic clocks. Improvements in measurement techniques now permit pulse arrival times to be determined in 1 hour at the Arecibo radio telescope with uncertainties of about 300 nanoseconds relative to atomic time. Measurements taken approximately every 2 weeks since November 1982 yield estimates of fractional frequency stability that continue to improve with increasing averaging time. The pulsar9s frequency stability is at least as good as 6 x 10 -14 for averaging times longer than 4 months, and over the longest intervals the measurements appear to be limited by the stability of the reference atomic docks. The data yield a firm upper limit of 7 x 10 -36 gram per cubic centimeter for the energy density of a cosmic background of gravitational radiation at frequencies of about 0.23 cycle per year. This limit corresponds to approximately 4 x 10 -7 of the density required to close the universe.

http://science.sciencemag.org/content/sci/238/4828/761.full.pdf

Millisecond Pulsar PSR 1937+21: A Highly Stable Clock.

Recent observations1,2 at the Arecibo Observatory have resulted in the discovery of PSR1855+09, a pulsar with period P=5.362 ms, moving in a nearly circular orbit of period 12.3 days. The pulsar is only the third one known with P < 10 ms, and the sixth known radio pulsar in a binary system. (Discovery of a seventh binary pulsar is announced in an accompanying paper3.) Three of the seven binaries are among the fastest five of more than 400 pulsars—a fact that provides strong support for the conclusion that fast pulsars are ‘recycled’ neutron stars, spun up during a phase of mass accretion from an evolving companion star. The pulsar has a small dispersion measure (13.3 cm−3 pc), suggesting a distance of only ∼350 pc. The proximity of this pulsar and its location within 25 pc of the galactic plane argue that millisecond pulsars form a significant fraction (∼10%) of the pulsar population, leaving many detectable ones undiscovered4,5. Its signal is strong enough to permit pulse-arrival-time measurements with single-day uncertainties of <3µs. Timing observations already suggest that PSR1855+09, like the 1.5-ms pulsar PS R1937+21, will prove to be a natural clock of extremely high stability6. The existence of a second pulsar with extremely small timing uncertainties will greatly aid the search for background gravitational waves using millisecond pulsars as detectors.

New millisecond pulsar in a binary system

Much of the interesting physics concerning neutron stars and their evolution depends for its experimental foundation on observations of the rotation rates of pulsars. To continue recent efforts of our group in this area1–3, we began a series of pulse-arrival-time observations of ∼70 pulsars in January 1985. Most of the pulsars in this study were discovered in the Princeton/NRAO pulsar survey of the preceding two years4,5. Soon after we began these observations it became clear that PSR2303+46 was a binary pulsar2; it is now evident that PSR1831–00 is also a member of a binary system, the seventh such radio pulsar known. It moves in an orbit with a period of 1.81 days, a small eccentricity, and an unusually small mass function of 0.00012 M⊙ (where M⊙ is the mass of the Sun). With a period P = 0.521 s and period derivative P≲ 10−17 s s−1, PSR1831–00, like the other known binary pulsars, has a relatively weak magnetic field. We discuss the features of this system that provide clues to its evolutionary history and outline possible models for its formation.

Binary pulsar with a very small mass function

PSR1953+29, the second fastest of more than 400 known pulsars1, has a period of 6.133 ms and is a member of a binary system with an orbital period of 117.35 days. The system is of great interest because of what it can reveal about the evolution of pulsars and close binary stars2–4. Recently we have carried out observations to determine two of the most important parameters of the system, the pulsar period derivative Ṗ and the orbital eccentricity e. We find a small but non-zero eccentricity, e =(330.3±0.4) × 10−6, and a spindown rate of Ṗ = (1±6)×10−20 s s−1, smaller than that measured for any other pulsar. These values are consistent with an evolutionary history involving spin-up during a mass accretion phase, but are difficult to reconcile with a recent report of periodically pulsed γ rays from this object5.

L. A. Rawley

Papers

Millisecond Pulsar PSR 1937+21: A Highly Stable Clock.

New millisecond pulsar in a binary system

Binary pulsar with a very small mass function

Period derivative and orbital eccentricity of binary pulsar 1953+29